Sen. Elizabeth Warren said Wednesday that she had "no doubt" that firing of FBI Director James Comey's is President Donald Trump's attempt to cover up any possible ties to Russia by him or his campaign.

"There's just no doubt, given the timing," the Massachusetts Democrat told Manu Raju on CNN. "The reason Comey was fired is that Donald Trump wants to cut off any investigation into any connections that he has with his campaign and his connections to the Russians."

Warren, 67, said that Deputy Attorney General Rod Rosenstein must now be subpoenaed to testify before Congress amid news reports that Comey was fired because he had asked for more funding for the Moscow probe.

"The Judiciary Committee should call him right now and have him testify under oath as to exactly what Comey asked for," she said. "That should be clear right now."

The first-term senator renewed her longstanding call for a special prosecutor in the Russian probe and said that any inquiry should be nonpartisan.

"I don't think it should be about what the Democrats are demanding," Warren told CNN. "It's about the American people wanting to see this — and everyone in Congress should get down to bottom of this."